Has anyone here documented the process for
*shooting in 50i pal,
*capturing in cineform (where there is a 4% slowdown option--that I do not fully understad)
*de-interlacing to 25p

It seems simple enough, but I'm wondering if anyone has already worked out all the hiccups.

Where are you running into difficulty? Deinterlacing can run from very simple (and easy) to quite sophisticated.

No issues yet. this is a project for when I return from a trade show (the end of this week). I just wanted to see if this process has already been hashed out. I didn't find anything by searching.

I guess you could say it's been hashed out, in that deinterlacing is done by many, and often. Deinterlacing isn't just one thingy. There are many methods, that range from very, very simple, to quite sophisticated.

Here's a link to a site that might be of interest to you:

http://www.100fps.com/